Sample bag

ABSTRACT

A sample bag for collecting a mixture of gasses for analysis is made of a modified polymer consisting essentially of tetrafluoroethylene (TFE) and at most about 2.0 percent perfluoropropylvinylether (PPVE).

TECHNICAL FIELD

[0001] The present invention relates to a sample bag for collecting amixture of gasses for analysis, and to a method of collecting a dilutedexhaust gas mixture from an internal combustion engine.

BACKGROUND ART

[0002] A gas diluting and testing apparatus is used to analyze, amongother things, vehicular exhaust. The apparatus uses a mixing system todilute the exhaust gasses so that the moisture content of the gasses issufficiently reduced in order to minimize errors due to condensation.One example of an existing mixing system is the constant volume sampler(CVS).

[0003] The CVS has been used for over twenty-five years to sample theemissions from automobiles. It is the device used for automotiveemissions tests that are the basis for the certification that vehiclessold in the United States are compliant with the Clean Air Act.

[0004] Automotive sampling systems, as well as other analytical systems,utilize sealed bags for collecting engine exhaust gasses for analysis ofcomponents after the collection interval has been completed. In order topreserve the integrity of the captured sample, the sample bag materialmust be inert, non-reactive, without leaks, and must have low permeationfor the specific gasses contained both within the bag and outside thebag. The sample bag must not emit or absorb gasses, and the bag materialmust be flexible for fill and empty cycling. In the past, materials usedfor construction of the sample bag walls have failed to meet one or moreof the above criteria, and it is desirable to provide a sample bag thatlimits these various undesirable characteristics. As vehicles becomecleaner, their emissions become more difficult to measure accurately. Toovercome some of the inherent limitations of the CVS, some attempts havebeen made to develop improved mixing systems. In addition to the effectsof the mixing system itself, mixing systems that collect a gas mixturewith a sample bag may sometimes be limited in accuracy due tolimitations of the sample bag.

[0005] Although many existing mixing systems and existing sample bagshave been used in applications that are commercially successful, withincreasing demands for more accurate measurement techniques, it isdesirable to make improvements to existing measurement and dilutiontechniques for analysis of gaseous constituents.

DISCLOSURE OF INVENTION

[0006] It is, therefore, an object of the present invention to provide asample bag for collecting a mixture of gasses for analysis that is madeof a modified polymer that limits the effects of diffusion through thebag walls and limits the effect of residual gasses within the bag wallson the integrity of the collected sample.

[0007] In carrying out the above object and other objects and featuresof the present invention, a sample bag for collecting a mixture ofgasses for analysis is provided. The sample bag is made of a modifiedpolymer consisting essentially of tetrafluoroethylene (TFE) and at mostabout 2.0 percent perfluoropropylvinylether (PPVE). The modified polymeris melt processable, unlike conventional polytetrafluoroethylene (PTFE).Because the modified polymer may be heat sealed and bonded to itself byvarious welding techniques, the modified polymer reduces the effects ofdiffusion through the sample bag walls and residual gasses in the samplebag walls.

[0008] The amount of perfluoropropylvinylether (PPVE) co-monomer in themodified polymer may vary depending on the desired properties for thesample bag. That is, the modified polymer for the sample bag consistsessentially of tetrafluoroethylene (TFE) and at most about 2.0 percentperfluoropropylvinylether (PPVE), and preferably, at most about 1.5percent perfluoropropylvinylether (PPVE). More preferably, the modifiedpolymer includes at most about 1.0 percent perfluoropropylvinylether(PPVE) co-monomer. More preferably, the modified polymer includes atmost about 0.3 percent perfluoropropylvinylether (PPVE). Morepreferably, the modified polymer includes at most about 0.2 percentperfluoropropylvinylether (PPVE) co-monomer. More preferably, themodified polymer includes at least about 0.05 percentperfluoropropylvinylether (PPVE) co-monomer. In a suitable application,the modified polymer includes about 0.1 percentperfluoropropylvinylether (PPVE). It is appreciated that the percentagesare mass percentages, as is readily understood by one skilled in thepolymer arts.

[0009] Further, in carrying out the present invention, a method ofcollecting a diluted exhaust gas mixture from an internal combustionengine is provided. The method comprises receiving an exhaust gasmixture, receiving a dilution gas, mixing the dilution gas with theexhaust gas mixture to form the diluted exhaust gas mixture, andcollecting the diluted gas exhaust gas mixture in a sample bag. Thesample bag is made of a modified polymer consisting essentially oftetrafluoroethylene (TFE) and at most about 2.0 percentperfluoropropylvinylether (PPVE). It is appreciated that the amount ofperfluoropropylvinylether (PPVE) co-monomer in the modified polymer mayvary depending on the particular desired properties for the sample bag.

[0010] Still further, in carrying out the present invention, a samplebag for collecting diluted exhaust gasses from an internal combustionengine is provided. The sample bag comprises a boundary structure and aninlet connected to the structure for receiving the gasses. The boundarystructure defines a container for the gasses. The structure is made of amodified polymer consisting essentially of tetrafluoroethylene (TFE) andat most about 2.0 percent perfluoropropylvinylether (PPVE). It isappreciated that the amount of perfluoropropylvinylether (PPVE)co-monomer may vary depending on the particular application andproperties desired for the sample bag.

[0011] The advantages associated with embodiments of the presentinvention are numerous. For example, a sample bag for collecting amixture of gasses for analysis that is made of the modified polymerconsisting essentially of tetrafluoroethylene (TFE) and at most about2.0 percent perfluoropropylvinylether (PPVE) reduces the effects ofdiffusion through the bag walls and the effects of residual gasses inthe bag walls (emission and absorption by the walls) on the integrity ofthe sample. That is, a sample bag made of the modified polymer overcomeslimitations associated with other sample bags including sample bags madeof pure polytetrafluoroethylene (PTFE).

[0012] The above object and other objects, features, and advantages ofthe present invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is a schematic diagram illustrating a CVS connected tosample bags of the present invention;

[0014]FIG. 2 is a front view of a sample bag of the present invention;

[0015]FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;and

[0016]FIG. 4 is a block diagram illustrating a method of the presentinvention for collecting a mixture in a sample bag made of a modifiedpolymer of TFE with a small amount of PPVE co-monomer.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] Referring to FIG. 1, a CVS is generally indicated at 10. CVS 10has a mixing portion 12, a gaseous inlet 14, a dilution inlet 16, and amixture outlet 18. A dilution sample line 20, a needle valve 22 and apump 24 cooperate to fill sample bags 26 with dilution gas.

[0018] Raw exhaust from the vehicle under test enters gaseous inlet 14and is mixed with dilution air. The mixed gasses are drawn through amain venturi 30 by a blower 32. Main venturi 30 is sonic, or choked, andmeters and measures the flow of the combined gasses. A mixture sampleline 34 connects to mixture outlet 18 through a smaller, sample venturi36 also operated in sonic or choked condition. A pump 38 cooperates withsample venturi 36 to fill sample bags 40 with the mixed gasses for lateranalysis.

[0019] Of course, it is appreciated that the sample bag of the presentinvention may be used in any suitable mixture collecting apparatus andis not limited to the specific CVS illustrated in FIG. 1. In accordancewith the present invention, the sample bags 26 and 40 are made of amodified polymer consisting essentially of tetrafluoroethylene (TFE) andat most about 2.0 percent perfluoropropylvinylether (PPVE). The modifiedpolymer of TFE with a small amount of PPVE co-monomer has improvedperformance over a sample bag made of pure PTFE. Specifically, whiledeveloping the present invention, PTFE film had been tested as materialfor the sample bag walls, and heated methods were used for fabricationwhich sealed the walls together. PTFE possesses some of the desiredqualities for a sample bag but has high permeability to some gasses ofinterest due to its method of manufacture. Specifically, the PTFE samplebags have high permeability to diluted exhaust gas mixtures that arecollected in automotive sampling systems.

[0020] Although PTFE sample bags have been used successfully becausemost forms of PTFE do not have a plastic or fluid phase, very smallvoids exist in the fabricated materials which allows gasses to betrapped within the material, and also allow the diffusion of gassesthrough the walls of the thin film itself. That is, when the sample bagsare made of pure PTFE, diffusion through the sample bag walls reducesthe integrity of the sample, and the bag walls may emit and absorbgasses, compromising the integrity of the present sample as well asfuture samples in the same sample bag. In accordance with the presentinvention, a modified polymer of PTFE with TFE and PPVE as co-monomersis used to make a sample bag. The improved material, unlike pure PTFE,may be melt processed, to fill the voids in the base product. Theresulting modified polymer material has significantly reducedpermeability to the gasses of interest and has reduced the presence ofvoids. so that the emission and absorption of gasses by the bag wallsthemselves is reduced. A suitable material for a sample bag of thepresent invention is known as TFM™ PTFE, and is available from DyneonLLC, Oakdale, Minn.

[0021] As shown in FIGS. 2 and 3, a sample bag 50 includes a boundarystructure 52 forming the sample bag walls. The boundary structuredefines a container for the gasses and is made of a modified polymerconsisting essentially of tetrafluoroethylene (TFE) and at most about2.0 percent perfluoropropylvinylether (PPVE). Of course, the amount ofPPVE may vary depending on the particular properties desired for thebag. It is to be appreciated that the small amount of PPVE co-monomerdramatically improves the properties of the sample bag walls. Forexample, the sample bag walls made of the modified polymer have improvedweldability, lower permeability, and other improved properties. At thesame time, the modified polymer still has many of the desirableproperties of pure PTFE such as chemical resistance and thermalstability. For sample bags of the present invention, it is appreciatedthat the denser polymer structure with lower permeability and fewervoids is very advantageous to reduce the effects of diffusion of gassesthrough the walls, and the emission and absorption of gasses into andout of the bag walls, in turn, providing an overall higher integrity ofthe gas sample collected in the bag than existing sample bags includingpure PTFE sample bags.

[0022] In FIG. 4, a method of the present invention is generallyindicated at 60. At block 62, an exhaust gas mixture is received. Atblock 64, a dilution gas is received. At block 66, the dilution gas andthe exhaust gas mixture are mixed to form a diluted gas mixture. Atblock 68, a diluted exhaust gas mixture is collected in the sample bag.The sample bag, in accordance with the present invention, is made of amodified polymer of TFE with a small amount of PPVE co-monomer.

[0023] While embodiments of the invention have been illustrated anddescribed, it is not intended that these embodiments illustrate anddescribe all possible forms of the invention. Rather, the words used inthe specification are words of description rather than limitation, andit is understood that various changes may be made without departing fromthe spirit and scope of the invention.

What is claimed is:
 1. A sample bag for collecting a mixture of gasesfor analysis, the sample bag being made of a modified polymer consistingessentially of tetrafluoroethylene and at most about 2.0%perfluoropropylvinylether.
 2. The sample bag of claim 1 wherein themodified polymer consists essentially of tetrafluoroethylene and at mostabout 1.5% perfluoropropylvinylether.
 3. The sample bag of claim 2wherein the modified polymer consists essentially of tetrafluoroethyleneand at most about 1.0% perfluoropropylvinylether.
 4. The sample bag ofclaim 3 wherein the modified polymer consists essentially oftetrafluoroethylene and at most about 0.3% perfluoropropylvinylether. 5.The sample bag of claim 4 wherein the modified polymer consistsessentially of tetrafluoroethylene and at most about 0.2%perfluoropropylvinylether.
 6. The sample bag of claim 5 wherein themodified polymer consists essentially of tetrafluoroethylene and atleast about 0.05% perfluoropropylvinylether.
 7. The sample bag of claim6 wherein the modified polymer consists essentially oftetrafluoroethylene and about 0.1% perfluoropropylvinylether.
 8. Amethod of collecting a diluted exhaust gas mixture from an internalcombustion engine, the method comprising: receiving an exhaust gasmixture; receiving a dilution gas; mixing the dilution gas with theexhaust gas mixture to form the diluted exhaust gas mixture; andcollecting the diluted exhaust gas mixture in a sample bag, the samplebag being made of a modified polymer consisting essentially oftetrafluoroethylene and at most about 2.0% perfluoropropylvinylether. 9.The method of claim 8 wherein the modified polymer consists essentiallyof tetrafluoroethylene and at most about 1.5% perfluoropropylvinylether.10. The method of claim 9 wherein the modified polymer consistsessentially of tetrafluoroethylene and at most about 1.0%perfluoropropylvinylether.
 11. The method of claim 10 wherein themodified polymer consists essentially of tetrafluoroethylene and at mostabout 0.3% perfluoropropylvinylether.
 12. The method of claim 11 whereinthe modified polymer consists essentially of tetrafluoroethylene and atmost about 0.2% perfluoropropylvinylether.
 13. The method of claim 12wherein the modified polymer consists essentially of tetrafluoroethyleneand at least about 0.05% perfluoropropylvinylether.
 14. The method ofclaim 13 wherein the modified polymer consists essentially oftetrafluoroethylene and about 0.1% perfluoropropylvinylether.
 15. Asample bag for collecting diluted exhaust gases from an internalcombustion engine, the sample bag comprising: a boundary structuredefining a container for the gases, the structure being made of amodified polymer consisting essentially of tetrafluoroethylene and atmost about 2.0% perfluoropropylvinylether; and an inlet connected to thestructure for receiving the gases .
 16. The sample bag of claim 15wherein the modified polymer consists essentially of tetrafluoroethyleneand at most about 1.5% perfluoropropylvinylether.
 17. The sample bag ofclaim 16 wherein the modified polymer consists essentially oftetrafluoroethylene and at most about 1.0% perfluoropropylvinylether.18. The sample bag of claim 17 wherein the modified polymer consistsessentially of tetrafluoroethylene and at most about 0.3%perfluoropropylvinylether.
 19. The sample bag of claim 18 wherein themodified polymer consists essentially of tetrafluoroethylene and at mostabout 0.2% perfluoropropylvinylether.
 20. The sample bag of claim 19wherein the modified polymer consists essentially of tetrafluoroethyleneand at least about 0.05% perfluoropropylvinylether.
 21. The sample bagof claim 20 wherein the modified polymer consists essentially oftetrafluoroethylene and about 0.1% perfluoropropylvinylether.